The association of changes in the metabolic pathway of monoamines (dopamine and 5-hydroxy-tryptamine) with mitochondrial enzyme systems which are involved in the production and removal of free radicals formed during dopamine metabolism and formation of edema was investigated in bilateral brain ischemia in gerbils. The results suggest that the involvement of dopamine-derived free radicals in brain edema is unlikely in early reflow, because imbalance between H2O2~producing reactions of dopamine metabolism and mitochondrial antioxidative capacity does not occur prior to 1 hr reflow after 15 min of bilateral ischemia in gerbils. However, the findings of this study reinforce the participation of 5- hydroxytryptamine in the formation of ischemic brain edema.